Blood concentrations of marbofloxacin and its in vivo effect in yellow-bellied slider turtles (Trachemys scripta scripta) after a single intracoelomic injection at 3 dose rates

Marbofloxacin is a common antibiotic drug used to treat bacterial infections in pet animals. Similar to other fluoroquinolones, marbofloxacin is subject to the emerging problem of antimicrobial resistance. Thus, it is necessary to use pharmacokinetic/pharmacodynamic (PK/PD) integration and modeling to minimize the selection of resistant mutants of bacteria and extend the useful life of antimicrobial agents, including marbofloxacin. This study evaluated the PKs and the in vivo efficacy of marbofloxacin in Trachemys scripta scripta after a single intracoelomic injection. Three groups of healthy adult turtles (n = 8 per group) were each treated with 0.4, 2, and 10 mg/kg of marbofloxacin. Blood samples and rectal swabs were collected to measure marbofloxacin concentrations in blood (using high-performance liquid chromatography with fluorescence detection validated method) and to evaluate in vitro antimicrobial susceptibility (using Kirby-Bauer Method), respectively. The PK profiles of marbofloxacin fit a bicompartmental model and were dose dependent. The Tmax and half-life ranged between 2.82 to 4.64 hours and 16.14 to 30.68 hours, respectively. Bacterial isolation showed the presence of both Escherichia coli and Salmonella spp. Salmonella spp. were isolated only 48 hours after the administration of marbofloxacin, and all strains were considered resistant. Results seem to suggest that even if marbofloxacin is able to reach considerable plasma concentrations, it can still be ineffective against bacteria that are potential animal and human pathogens.